Recovery of copper and steel from scrap

ABSTRACT

Scrap items containing copper and iron in physical admixture, such as electrical and electronic scrap, are pretreated with an aqueous reagent, such as an alkali metal sulfate or silicate, prior to recovery of the copper by preferential melting in an inert, liquid medium. The chemical pretreatment reduces the tendency of copper to alloy or braze with the iron and results in a substantially higher copper recovery in the preferential melting step.

nite States Patent [191 et al.

[ Dec.4,1973

[ RECOVERY OF COPPER AND STEEL FROM SCRAP [75] Inventors: Vance G. Leak;Morris M. Fine,

both of Minneapolis, Minn.

[73] Assignee: The United States of America as represented by theSecretary of the Interior, Washington, DC.

[22] Filed: July 13, 1972 21 App]. No.: 271,340

[52] US. Cl 75/63, 75/65, 75/72 [51] Int. Cl. C22b 7/00, C22b 15/00 [58]Field of Search 75/72, 65, 63

[56] References Cited UNITED STATES PATENTS l/l972 Foard 75/72 OTHERPUBLICATIONS Secondary Raw Materials Vol. 6, No. 7 July 1968 pp.

Primary ExaminerA. B. Curtis Assistant Examiner-Mark Bell AttorneyErnestS. Cohen et al.

57 ABSTRACT 13 Claims, No Drawings 1 RECOVERY OF COPPER AND STEEL FROMSCRAP BACKGROUND OF THE INVENTION Iron and copper are fabricated intointricate mechanical composites in the production of electrical andelectronic components. Examples include motor armatures, field cores,transformers, copper-clad wire and a host of other electrical andelectronic devices. Both the copper and the iron (often high-siliconsteel) contained in such devices have a high scrap value but eachmaterial is a deleterious contaminant of the other. It is not practicalwith=present.technologyto make a clean separation of the two materialsexcept by tedious handdisassembly. Since processing economics is usuallythe sole consideration in determining whether to recover secondarymetals from particular scrap commodities, much electrical and electronicscrap is at 'thistime'discarded rather thanbeing reclaimed.

Preferential melting or sweating techniques would seem to be anappropriate-means for separatingcopper and steel considering thewidespread in melting points, 1,083" and about .1 ,450 C,.respectively.Sweating techniques are effective in reclaiming the low-melting pointmetals, such as lead, tin, zinc and aluminum, and have been commerciallyused for some time; However, experiments in gaseous combustionatmospheres showed that ordinary sweating procedures were notsatisfactory for the copper-iron system due to oxidation of iron andentrapment of copper within the oxide scale. A reducing atmospherediminishes scaling but enhances the tendency for copper to alloy withiron.

In our previous work, we discovered that if the sweating is accomplishedin a neutral molten substance such as barium chloride, both oxidationand alloying of cop-' per and iron arelessened and the liquid bathpromotes rapid heat transfer. This technique wasshown to be useful forreclaiming the components of copper-iron scrap items such as armatures,some types of electronic scrap and gilding metal. A report on thisprevious work was published in Secondary. Raw Materials, Vol. 6, No. 7,July 1968, pages 27-29. Although this technique constituted aconsiderable improvement over conventional sweating methods, theresidual iron (suchas the steel core of scrap armatures) stillretainedseveral percent of copper.

SUMMARY OF THEINVENTION We can achieve a nearly quantitative separationof copper from iron by first pretreating scrap with selected chemicalreagents prior to preferentially melting the copper in a neutral, moltenmedium. These chemical reagents alter and coat the surface of the ironso it is less subject to brazing in the molten bath. It. is believedthat these reagents render the iron less susceptible to alloying withcopper either by controlled, mild oxidation or by coating the ironsurface with a nonreactive substance. Preferred reagents include thealkali metal sulfates and silicates.

It is therefore an object of our invention to separate copper from iron.

A specific object of our-invention is to reduce the alloying of copperwith iron in those separation processes in which copper ispreferentially melted and separated from copper-iron scrap.

Another object of our invention is to increase the copper recovery andincrease its purity by the preferen- .2 tial melting of copper,contained in copper-iron scrap by immersion in a molten, inert, liquidmedium.

DETAILED DESCRIPTION OF THE INVENTION Our invention comprises thechemical pretreatment of copper-iron scrap commodities followed bypreferential melting and separation of the copper in a molten mediumbath. Chemical pretreatment is accomplished by coating the scrap with areagent which preventsor inhibits the alloying or-brazing of copper withiron. Preferredchemical reagents comprise the alkalimetal sulfates andsilicates. We particularly prefer sodium sulfate and sodium silicate asreagents-in our process.

The pretreatmentmay be accomplished by immersing scrap components into areagent solution or by spraying or brushingthe solution onto thecomponents.

' It is unimportanthow the reagent is applied as long as step desirablyincluded in order to reduce the heat requirement of the molten bath.

While we have found the alkali metal sulfates and silicates to begenerally useful in our process, we prefer sodium sulfate and sodiumsilicates primarily because of their availability and economy. Sodiumsilicates generally are operative in our process so long as they arewater soluble. Ratio of Na O to SiO contained in the silicate reagentappears to have little if any effect on the process. Useful forms ofsodium silicate include but are not limited to sodium disilicate, sodiummetasilicate and sodium orthosilicate as well as the sodium silicatecommonly referred to as water glass. The reagent may be made up for useas an aqueous solution conveniently having a concentration in the rangeof about 5 percent to 60 percent. Temperature at which scrap componentsaretreated with the reagent solution is unimportant but from a practicalviewpoint should be below the boiling point of the solution. Mostconveniently, treatment temperature should be ambient or slightly above.

In practicing our invention, the molten medium used in preferentiallymelting copper may be any salt, slag or glass which is stable,noncorrosive, and relatively nonvolatile at a temperature above themelting point of copper. In addition, the medium preferably isrelatively inexpensive. Materials such as silicate slags (from ironfoundries and copper smelting) barium chloride, calcium chloride and thelike are well suited for use as the molten medium. Commercialheat-treating salts for high-speed steel were also used successfully;these are proprietary mixtures with barium chloride as a principalcomponent. The temperature range in which the preferential melting ofcopper may be carried out is limited to a temperature above the meltingpoint of copper and below the melting point of iron, or from about l,083to l,450 C. We prefer to operate in the lower portion of that range orfrom about l,l00 to l,300 C. Higher temperature operation increases thetendency of copper to alloy with iron, increases medium losses due tovolatilization and increases the heat requirements of the process.

Apparatus suitable for use in the preferential melting step of ourprocess may comprise commercial furnaces rium temperature. This requireda minute or two after which the armature was soaked in the bath for atime such as those salt bath furnaces used in heat treating 5 periodranging from about 1 to minutes. Copper steel articles. These furnacesare typically internally droplets sweated from the scrap and collectedin the heated by electrical resistance and are capable of conbottom ofthe crucible. The armature was then shaken tinuous service attemperatures as high as 1,300 C. If to remove adhering salt and moltencopper, then desired, these standard furnaces may be modified to droppedon a hard surface to further reduce adhering provide a semi-continuousdischarge of molten copper l0 liquid. An analysis for copper was thenperformed on by providing suitable tapping means in the lower poreach ofthe steel armature cores. Results obtained in non of the salt pot. thesetests are summarized in the following table.

TABLE 1 Residual analysis of steel cores, percent Cu Copper 10st insteel cores, percent of total Separating Temp,

Test number media C. No pre-treat. NazSOt dip NazSiO; dip N0 pro-treat.NazSOi dip NazSiO; dlp

B11012 1,150 2.75 0.27 0.14 0.9 0.8 0.5 B11012 1, 200 5. 10 o. 0.12 12.7 0. 6 0. 3 H1101; 1,250 5. 71 0. 37 0.13 21. 4 1. 0 0. 7 c501, 1,1506.98 1.74 3.33 10.0 4.0 9.1 08015 1,200 4.75 3. 64 2. 50 15 6 8.7 7.21,250 4.69 3.5 0.3

A general procedure for carrying out our process is as follows. Scrapitems containing copper and iron such as motor armatures or electronicscrap are first cleaned and degreased if necessary. The clean scrap isthen dipped into the aqueous reagent solution and thoroughly dried.Preheating of scrap items to a temperature of several hundred degreesCentigrade may follow or form a part of the drying operation if desired.The scrap items are then immersed in a molten medium, such as bariumchloride, maintained at a temperature above about l,l00 C. Immersiontime must be sufficient to melt the contained copper and is typically inthe range of about 1 to 15 minutes. Stainless steel mesh baskets haveproven satisfactory to hold the scrap components during the immersion.The basket, retaining the iron portion of the scrap items, is thenremoved from the bath and is shaken or vibrated to remove any adheringliquid medium or molten copper. Copper sinks to the bottom of the bathwhere it remains in the liquid state and may be periodically tapped. Thecopper product analyzes 96 percent or more copper with the balance beingmostly iron and small percentages of lead, zinc, aluminum and the likedepending upon the scrap being processed. Residual copper content of theiron depends to some extent on the scrap items processed and upon thecomposition of the molten medium but will generally range from about 0.1to about 3 percent.

The following examples illustrate specific embodiment of our invention.

EXAMPLE 1 A number of small (l-% in. diameter) armatures were dividedinto three lots. One lot was treated by dipping in a saturated solutionof sodium sulfate, a second lot was treated by dipping in a saturatedsolution of sodium silicate, while the third lot was not treated. Thearmatures were then dried at about 100 C. A series of preferentialmelting tests were run on each lotusing barium chloride and calciumchloride as the molten medium, at temperatures of l,l5(), l,200 andl,250 C.

A graphite crucible, heated by an induction furnace, was used to holdthe liquid medium. Temperature was measured with an optical pyrometer. Amotor arma- As may be seen from the data, our pretreatment spectacularlyimproves the recovery of copper when 25 barium chloride is used as themolten medium. Gains realized by the pretreatment using calcium chlorideas the molten medium are not as great but are still substantial.Although the barium chloride medium proved superior from a technicalviewpoint, there may be advantages in the use of calcium chloridebecause of its lower price. Both the barium chloride and calciumchloride baths were reused many times without apparent change in theircharacteristics.

EXAMPLE 2 We evaluated our technique in the recovery of copper from amixed group of copper-base electronic components using a barium chloridebath. The components were placed in a stainless steel mesh basket andwere immersed in the bath for 5 minutes at 1,250 C. Copper recoveredamounted to 85.7 percent of the input weight with 0.9 percent ironpresent as an impurity. Copper recovery was lower with electroniccomponents than with armatures because of their greater physicalcomplexity.

EXAMPLE 3 Salt mediums were prepared using barium chloride as a majorcomponent with sodium sulfate being added in amounts of 5, l0 and 20percent. The salts were then evaluated as a molten medium for use in thepreferential melting of copper. Test objects were armatures as inExample 1 and the procedure of that example was followed except that thearmatures were not chemically pretreated. Object of these tests was todetermine whether sodium sulfate would function as a bath component inthe same way it functioned as a pretreating reagent. Performance of thebarium chloride-sodium sulfate salt mictures was essentially equivalentto that of barium chloride alone. Sodium sulfate incorporated into thebath did not display the alloy inhibiting action exhibited when it wasused in aqueous solution as a pretreating reagent.

We claim:

1. A process for recovering copper from composite scrap items containingelemental copper and iron in physical admixture which comprises:

coating the scrap items with an aqueous solution of a chemical reagentwhich renders the iron less susceptible to alloying with copper;

drying the coated scrap items;

immersing the dried coated scrap items in a neutral molten mediummaintained at a temperature above the melting point of copper but belowthe melting point ,of iron for a time sufficient to preferentially meltthe elemental copper contained in the composite scrap items; and

separating the molten copper from the unmelted iron portion of thecomposite scrap items.

2. The process of claim 1 wherein the chemical reagent is chosen fromthe group consisting of alkali metal sulfates and alkali metalsilicates.

3. The process of claim 2 wherein the molten medium is stable andrelatively non-volatile at temperatures above the melting point ofcopper.

4. The process of claim 3 wherein the molten medium is chosen from thegroup consisting of salts, slags and, glasses.

5. The process of claim 4 wherein the molten medium is maintained at atemperature within the range of 1,100 to l,300 C.

6. The process of claim 5 wherein the chemical reagent is chosen fromthe group consisting of sodium sulfate and sodium silicates.

7. The process of claim 6 wherein the scrap items are treated by dippingin a relatively concentrated reagent solution.

8. The process of claim 6 wherein the medium com prises calcium chlorideand wherein the reagent is sodium sulfate.

9. The process of claim 6 wherein the medium comprises calcium chlorideand wherein the reagent comprises sodium silicate.

10. The process of claim 6 wherein the medium comprises barium chlorideand wherein the reagent is sodium sulfate.

11. The process of claim 6 wherein the medium comprises barium chlorideand wherein the reagent comprises sodium silicate.

12. The process of claim 6 wherein the scrap items are suspended in aperforated steel basket during immersion in the molten medium.

13. The process of claim 6 wherein the molten medium is contained withina crucible-type furnace and wherein molten copper is collected at thebottom of the crucible.

2. The process of claim 1 wherein the chemical reagent is chosen fromthe group consisting of alkali metal sulfates and alkali metalsilicates.
 3. The process of claim 2 wherein the molten medium is stableand relatively non-volatile at temperatures above the melting point ofcopper.
 4. The process of claim 3 wherein the molten medium is chosenfrom the group consisting of salts, slags and glasses.
 5. The process ofclaim 4 wherein the molten medium is maintained at a temperature withinthe range of 1,100* to 1,300* C.
 6. The process of claim 5 wherein thechemical reagent is chosen from the group consisting of sodium sulfateand sodium silicates.
 7. The process of claim 6 wherein the scrap itemsare treated by dipping in a relatively concentrated reagent solution. 8.The process of claim 6 wherein the medium comprises calcium chloride andwherein the reagent is sodium sulfate.
 9. The process of claim 6 whereinthe medium comprises calcium chloride and wherein the reagent comprisessodium silicate.
 10. The process of claim 6 wherein the medium comprisesbarium chloride and wherein the reagent is sodium sulfate.
 11. Theprocess of claim 6 wherein the medium comprises barium chloride andwherein the reagent comprises sodium silicate.
 12. The process of claim6 wherein the scrap items are suspended in a perforated steel basketduring immersion in the molten medium.
 13. The process of claim 6wherein the molten medium is contained within a crucible-type furnaceand wherein molten copper is collected at the bottom of the crucible.